1. Field of the Invention
This invention relates generally to oral compositions for removing tooth stains, and more particularly, to enzyme enhanced silica abrasive containing dental compositions effecting stain removal from teeth.
2. The Prior Art
Many substances that a person confronts or comes in contact with on a daily basis can xe2x80x9cstainxe2x80x9d one""s teeth. In particular, foods, and fluids such as tea and coffee that one consumes tend to stain one""s teeth. These products or substances tend to accumulate on the enamel layer of the tooth and form a pellicle film over the teeth. These staining and discoloring substances can then permeate the enamel layer. This problem occurs gradually over many years, but imparts a noticeable discoloration of the enamel of one""s teeth.
Synthetically produced silicas incorporated in dentifrice compositions act as an abrasive to debride and physically scrub the external surface of the teeth. This scrubbing action removes the organic film (i.e. the pellicle), formed of salivary proteins which covers the teeth and which become stained and discolored. Such physical removal of the stained pellicle is a simple and effective means of removing the undesirable surface staining and discoloration which occurs daily.
Synthetic silicas useful as dentifrice abrasives include both silica gels and precipitated silicas which are prepared by the neutralization of aqueous silicate solutions with a strong mineral acid. In the preparation of silica gel, a silica hydrogel is formed which is then typically washed to a low salt content. The washed hydrogel may be milled to the desired size, or otherwise dried, ultimately to the point where its structure no longer changes as a result of shrinkage. When preparing such synthetic silicas, the objective is to obtain abrasives which provide maximal cleaning (i.e. removal of stained pellicle) with minimal damage to the tooth enamel and other oral tissue.
U.S. Pat. No. 4,153,680 and GB Patent Application 2,038,303A both disclose the general use of silica hydrogels or hydrated silica gels as dental abrasives.
U.S. Pat. No. 5,939,051 discloses dentifrice compositions prepared with silica gels having low abrasion and high cleaning properties.
U.S. Pat. Nos. 5,658,553 and 5,651,958 disclose dentifrice compositions containing a combination of precipitated silica and silica gels having high cleaning and low abrasion as indicated by their low radioactive dentin abrasion (RDA) values.
Copending patent application U.S. Ser. No. 09/567,402 filed May 9, 2000 discloses a silica hydrogel containing about 10 to about 35% by weight water, whereby the dentifrice composition has an RDA of from 110 to 200, and a PCR of from about 150 to about 300.
In spite of the extensive prior art relating to silica hydrogels and other abrasive compounds used to prepare dentifrice compositions for oral cleaning and stain removal, there is still a need for additional compositions providing improved pellicle cleaning and stain removal.
In accordance with the present invention there is provided a silica abrasive dentifrice composition which exhibits heightened tooth stain removal which composition comprises an orally acceptable vehicle containing a combination of a low oil absorption silica abrasive having an oil absorption value of less than 100 cubic centimeters (cc)/100 grams (g) silica and a proteolytic enzyme.
Low Oil Absorption Silica Abrasives
Silica abrasives useful in the practice of the present invention include silica gels and precipitated amorphous silica having an oil absorption value of less than 100 cc/100 g silica and preferably in the range of from about 45 cc/100 g to less than about 70 cc/100 g silica. These silicas are colloidal particles having an average particle size ranging from about 3 microns to about 12 microns, and more preferably between about 5 to about 10 microns and a pH range from 4 to 10 preferably 6 to 9 when measured as a 5% by weight slurry.
Oil absorption values are measured using the ASTM Rub-Out Method D281. The low oil absorption silica abrasive is present in the oral are compositions of the present invention at a concentration of about 5 to about 40% by weight and preferably about 10 to about 30% by weight.
Low oil absorption silica abrasives particularly useful in the practice of the present invention are marketed under the trade designation Sylodent XWA by Davison Chemical Division of W. R. Grace and Co., Baltimore, Md. 21203. Sylodent 650 XWA, a silica hydrogel composed of particles of colloidal silica having a water content of 29% by weight averaging from about 7 to about 10 microns in diameter, and an oil absorption of less than 70 cc/100 g of silica is a preferred example of a low oil absorption silica abrasive useful in the practice of the present invention.
Another low oil absorption silica abrasive particularly useful in the practice of the present invention is marketed under the trade designation DP-105 by J. M. Huber Chemicals Division, Havre de Grace, Md. 21078 is a precipitated amorphous silica having an average particle size distribution from 5 to 12 microns and an oil absorption in the range of 50 to 70 cc/100 g.
The low oil absorption silica abrasive can be used as the sole abrasive in preparing the dentifrice composition of the present invention or in combination with other known dentifrice abrasives or polishing agents.
Commercially available abrasives which may be used in combination with the low oil absorption silica abrasive include precipitated silicas having a mean particle size of up to about 20 microns, such as Zeodent 115, marketed by J. M. Huber Chemicals Division, Havre de Grace, Md. 21078, or Sylodent 783 marketed by Davison Chemical Division of W. R. Grace and Company. Other useful dentifrice abrasives include sodium metaphosphate, potassium metaphosphate, tricalcium phosphate, dihydrated dicalcium phosphate, aluminum silicate, calcined alumina, bentonite or other siliceous materials, or combinations thereof.
The total quantity of abrasive present in the dentifrice compositions of the present invention is at a level of from about 5% to about 40% by weight, preferably from about 5% to about 30% by weight when the dentifrice composition is a toothpaste.
Enzymes
The proteolytic enzymes useful in the practice of the present invention are those well known protein substances within the class of proteases, which breakdown or hydrolyze proteins (proteases). The proteolytic enzymes are obtained from natural sources or by the action of microorganisms having a nitrogen source and a carbon source. Examples of proteolylic enzymes useful in the practice of the present invention include papain, bromelain, chymotrypsin, ficin and alcalase.
Papain obtained from the milky latex of the Papaya tree is the proteolytic enzyme preferred for use in the practice of the present invention and is incorporated in the oral care composition of the present invention in an amount of about 0.1 to about 10% by weight and preferably about 0.5 to about 5% by weight, such papain having an activity of 150 to 300 units per milligram as determined by the Milk Clot Assay Test of the Biddle Sawyer Group (see J. Biol. Chem., vol. 121, pages 737-745).
Enzymes which may beneficially be used in combination with the proteolytic enzymes include carbohydrases such as glucoamylase, alpha-amylase, beta-amylase, dextranase and mutanase and lipases such as plant lipase, gastric lipase and pancreatic lipase.
Glucoamylase is a saccharifying glucoamylase of Aspergillus niger origin. This enzyme can hydrolyze both the alpha-D-1,6 glucosidic branch points and the alpha-1,4 glucosidic bonds of glucosyl oligosaccharides. The product of this invention comprises about 0.001 to 10% of the carbohydrases. The lipase enzyme used in this invention is derived from a select strain of Aspergillus niger. The enzyme has maximum lipolytic activity at pH 5.0 to 7.0 when assayed with olive oil. The enzyme has 120,000 lipase units per gram.
The carbohydrases and lipases may be included in the dentifrice composition at a concentration of about 0.10 to about 5.0% by weight and preferably about 0.2 to about 2% by weight. Among the carbohydrases useful in accordance with this invention are glucoamylase, alpha and beta-amylase, dextranase and mutanase.
Dentifrice Vehicle
The orally-acceptable dentifrice vehicle used to prepare the dentifrice composition comprises a water-phase, containing a humectant therein. The humectant is preferably glycerin, sorbitol, xylitol, and/or propylene glycol of molecular weight in the range of 200 to 1,000; but, other humectants and mixtures thereof may also be employed. The humectant concentration typically totals about 5 to about 70% by weight of the oral composition.
Reference hereto to sorbitol refers to the material typically commercially available as a 70% aqueous solution. Water is present typically in amount of at least about 10% by weight, and generally about 25 to 70% by weight of the oral composition. Water employed in the preparation of commercially suitable toothpastes should preferably be deionized and free of organic impurities. These amounts of water include the free water which is added plus that which is introduced with other materials such as with sorbitol.
The dentifrice compositions of the present invention can contain a variety of optional dentifrice ingredients. As described below, such optional ingredients can include, but are not limited to, thickening agents, surfactants, a source of fluoride ions, a synthetic anionic polycarboxylate, a flavoring agent, antibacterial agents, antitartar and coloring agents.
Thickening Agents
Thickeners used in the compositions of the present invention include natural and synthetic gums and colloids. Not all naturally occurring polymer thickeners (such as cellulose or carrageenans) are compatible with dentifrice ingredients (specifically enzymes) of dentifrice compositions when formulated in the presence of proteolytic enzymes. Thickeners compatible with proteolytic enzymes include xanthan gum, polyglycols of varying molecular weights sold under the tradename Polyox , and polyvinylpyrrolidone. Compatible inorganic thickeners include amorphous silica compounds which function as thickening agents and include colloidal silicas compounds available under the trade designation Cab-o-sil manufactured by Cabot Corporation and distributed by Lenape Chemical, Bound Brook, N.J.; Zeodent 165 from J. M. Huber Chemicals Division, Havre de Grace, Md. 21078; and Sylodent 15, available from Davison Chemical Division of W. R. Grace Corporation, Baltimore, Md. 21203. Other inorganic thickeners include natural and synthetic clays, lithium magnesium silicate (laponite) and magnesium aluminum silicate (Veegum).
The thickening agent is present in the dentifrice composition in amounts of about 0.1 to about 10% by weight, preferably about 0.5 to about 4.0% by weight.
Surfactants
Surfactants are used in the compositions of the present invention to achieve increased prophylactic action and render the dentifrice compositions more cosmetically acceptable. The surfactant is preferably a detersive material which imparts to the composition detersive and foaming properties.
Anionic surfactants such as higher alkyl sulfates such as sodium lauryl sulfate are not compatible with enzymes. Anionic surfactants facilitate denaturing of the enzyme and loss in activity. As a result, it is important to the practice of the present invention to use a surfactant or combination of surfactants that are compatible with the enzymes present in the toothpaste formulation and provide the requisite foaming characteristics. Examples of enzyme compatible surfactants include nonanionic polyoxyethylene surfactants such as Polyoxamer 407, Steareth 30, Polysorbate 20, and PEG-40 castor oil and amphoteric surfactants such as cocamidopropyl betaine and cocamidopropyl betaine lauryl glucoside. Preferred surfactants include a combination of Polyoxamer 407, polysorbate 20, PEG-40 castor oil and cocamidopropyl betaine at a total surfactant concentration in the dentifrice composition of between about 2 to about 10% by weight and preferably between about 3.5 to about 6.5% by weight at weight ratios of 2.5 Polyaxomer 407, 2.5 PEG-40 castor oil, 3.3 Polysorbate-20 and 1.0 cocamidopropyl betaine.
Fluoride and Other Active Agents
The dentifrice composition of the present invention may also contain a source of fluoride ions or fluorine-providing component, as anticaries agent in amount sufficient to supply about 25 ppm to 5,000 ppm of fluoride ions and include inorganic fluoride salts, such as soluble alkali metal salts. For example, preferred fluoride sources which are compatible with enzymes present in the composition are sodium fluoride, potassium fluoride, sodium fluorosilicate, ammonium fluorosilicate, as well as tin fluorides, such as stannous fluoride and stannous chloride. Sodium fluoride is preferred.
In addition to fluoride compounds, there may also be included antitartar agents such as pyrophosphate salts including dialkali or tetraalkali metal pyrophosphate salts such as Na4P2O7, K4P2O7, Na2K2P2O7, Na2H2P2O7 and K2H2P2O7 long chain polyphosphates such as sodium hexametaphosphate and cyclic phosphates such as sodium trimetaphosphate. These antitartar agents are included in the dentifrice composition at a concentration of about 1 to about 5% by weight.
Another active agent useful in dentifrice compositions of the present invention are antibacterial agents, which can be from 0.2 to 1.0% by weight of the dentifrice composition. Such useful antibacterial agents include non-cationic antibacterial agents which are based on phenolic or bisphenolic compounds, such as halogenated diphenyl ethers such as Triclosan (2,4,4xe2x80x2-trichloro-2xe2x80x2-hydroxydiphenyl ether).
Enzyme Stabilizing Agents
The dentifrice composition of the present invention may also contain ingredients which stabilize enzymes in a dentifrice environment. These stabilizers protect the enzyme from inactivation by chelating metal impurities present in the dentifrice composition which have the propensity to denature the active site of the enzyme by protecting the enzyme from oxidation. Chelating agents include, ethylene diamine tetraacetic acid (EDTA) and sodium gluconate at concentrations between 0.01 and 1%, preferably between 0.1 and 0.5%. Agents stabilizing the enzyme against oxidation include sodium bisulfite, metal gallates, sodium stannate and ascorbic acid at concentrations between about 0.1 and about 1.5%, preferably between about 0.3 and about 0.75%.
Anionic Polycarboxylate
Synthetic anionic polycarboxylates may also be used in the dentifrice compositions of the present invention as an efficacy enhancing agent for any antibacterial, antitartar or other active agent within the dentifrice composition. Such anionic polycarboxylates are generally employed in the form of their free acids or preferably partially or more preferably fully neutralized water soluble alkali metal (e.g. potassium and preferably sodium) or ammonium salts. Preferred are 1:4 to 4:1 copolymers of maleic anhydride or acid with another polymerizable ethylenically unsaturated monomer, preferably methylvinylether/maleic anhydride having a molecular weight (M.W.) of about 30,000 to about 1,800,000 most preferably about 30,000 to about 700,000. Examples of these copolymers are available from GAF Corporation under the tradename Gantrez, e.g. AN 139 (M.W. 500,000), AN 119 (M.W. 250,000); S-97 Pharmaceutical Grade (M.W. 700,000), AN 169 (M.W. 1,200,000-1,800,000), and AN 179 (M.W. above 1,800,000); wherein the preferred copolymer is S-97 Pharmaceutical Grade (M.W. 700,000).
When present, the anionic polycarboxylates is employed in amounts effective to achieve the desired enhancement of the efficacy of any antibacterial, antitartar or other active agent within the dentifrice composition. Generally, the anionic polycarboxylates is present within the dentifrice composition from about 0.05% to about 4% by weight, preferably from about 0.5% to about 2.5% by weight.
Flavor
The dentifrice composition of the present invention may also contain a flavoring agent. Flavoring agents which are used in the practice of the present invention include essential oils as well as various flavoring aldehydes, esters, alcohols, and similar materials. Examples of the essential oils include oils of spearmint, peppermint, wintergreen, sassafras, clove, sage, eucalyptus, marjoram, cinnamon, lemon, lime, grapefruit, and orange. Also useful are such chemicals as menthol, carvone, and anethole. Of these, the most commonly employed are the oils of peppermint and spearmint.
The flavoring agent is incorporated in the dentifrice composition at a concentration of about 0.1 to about 5% by weight and preferably about 0.5 to about 1.5% by weight.
Other Ingredients
Various other materials may be incorporated in the dentifrice compositions of this invention, including desensitizers, such as potassium nitrate; whitening agents, such as hydrogen peroxide, calcium peroxide and urea peroxide; preservatives; silicones; and chlorophyll compounds. These additives, when present, are incorporated in the dentifrice composition in amounts which do not substantially adversely affect the properties and characteristics desired.
Preparation of the Dentifrice
The preparation of dentifrices is well known in the art by reference. More specifically, to prepare a dentifrice of the present invention, generally the humectants e.g. glycerin, sorbitol, propylene glycol, and polyethylene glycol; are dispersed in the water in a conventional mixer under agitation. Into the dispersion are added the enzyme or enzymes organic thickeners, such as xanthan gum; any anionic polycarboxylate; any salts, such as sodium fluoride anticaries agents; tetrasodium pyrophosphate, sodium tripolyphasphate anticalculus salts and any sweeteners; the resultant mixture is agitated until a homogeneous gel phase is formed. Into the gel phase are added a pigment such as TiO2, and any acid or base required to adjust the pH. These ingredients are mixed until a homogenous phase is obtained. The mixture is then transferred to a high speed/vacuum mixer; wherein, the inorganic silica thickener, such as Zeodent 165; and surfactant ingredients are added to the mixture. The low oil absorption silica abrasive is added at this point, along with other abrasives to be used in the composition. Any water insoluble antibacterial agent, such as Triclosan, is solubilized in the flavor oils to be included in the dentifrice and the solution is added along with the surfactants to the mixture, which is then mixed at high speed for from 5 to 30 minutes, under vacuum of from about 20 to 50 mm of Hg, preferably about 30 mm Hg. The resultant product is in each case a homogeneous, semi-solid, extrudable paste or gel product.